Experimental Investigation of the Effectiveness of Hybrid FRP–Strengthened RC Columns on Axial Compression–Bending Interaction Behavior

Abstract

This research work presents the interaction behavior of square reinforced concrete (RC) columns strengthened with different fiber-reinforced polymer (FRP) techniques, namely, near-surface mounting (NSM), external bonding (EB), and hybrid strengthening (HYB). Hybrid FRP strengthening uses a combination of near-surface mounted FRP laminates, confined laterally using externally bonded FRP composites, to achieve significant improvement in the peak strength and ductility under all combinations of axial compression (P) and bending (M) loads. Different levels of eccentricity (e) normalized to the depth (h) were considered, such as (1) axial compression (e/h=0), (2) low-eccentricity compression (e/h=0.15), (3) high-eccentricity compression (e/h=0.63), and (4) pure bending (e/h=∞). A normalized axial compression–bending interaction diagram for the tested columns was developed based on the test results. Experimental results reveal that hybrid FRP strengthening of columns improves the peak strength considerably under all loading combinations of axial compression and bending. In hybrid specimens, bond failure of NSM-strengthened RC elements was prevented through the effective lateral confinement provided by EB carbon fiber–reinforced polymer (CFRP) fabric. The axial compression–bending interaction diagram was analytically derived using a strain compatibility procedure. Analytical predictions exhibited good correlation with the test results for all strengthening techniques.